Additive manufacturing by selective liquid cooling

ABSTRACT

A method of additively manufacturing parts by selectively cooling a liquefied thermoplastic material.

FIELD OF THE INVENTION

This invention relates to methods of additive manufacturing.

BACKGROUND OF THE INVENTION

It is well known that it is difficult to additively manufacture at high speed and high resolution with engineered thermoplastics. FDM (fused deposition modeling) additive manufacturing has made its way to production manufacturing using engineered polymers, but it suffers from low speeds for high resolution parts. FDM machines that can print much faster using larger extrusion nozzles have improved the speed dilemma, but suffer from parts of low resolution. DLP (digital light processing) additive manufacturing using light cured polymers has shown much promise for increasing the speed of manufacture with high resolution, but it suffers from polymer costs too high for production manufacturing and polymers that may degrade in the presence of light. All existing additive manufacturing technology adds energy to the liquid to polymerize it, using lasers, radiation, light, etc.

SUMMARY OF THE INVENTION

This invention seeks to solve the challenges presented by the prior art by using selective cooling of a layer of liquefied thermoplastic to make high resolution parts at high speed. The present invention differs from the prior art in that it removes energy from the liquid polymer to solidify it.

According to an embodiment of the invention, consecutive layers of heated liquefied thermoplastic are placed in a build tray which has or is in contact with a matrix of heat exchange elements, each of which may be selectively and independently heated and cooled. These elements use the Peltier thermoelectric effect to operate between cold and hot modes quickly. Peltier-type hot/cold junctions are one example of devices that may be used as these elements. These junctions are currently available to industry in cells as small as 3 mm². Peltier P and N junction “pellets,” the smallest operational unit size, can currently be produced down to fractions of a millimeter, and it is expected that thin film designs will soon make it possible to create a hot/cold zone measured in micrometers. This will allow the present invention to surpass resolution of even the best DLP printer today.

In a first step according to a method of the invention, a layer of thermoplastic is placed in the build tray and all of the elements in the matrix are caused to heat the build tray so as to liquefy the layer of thermoplastic above and in contact with them. A cooled platen is then lowered onto the liquefied thermoplastic creating a liquid interface between both the heat/cool element matrix and platen. The heat/cool element matrix is then controlled to cool only the elements where the part is to be formed. This cools the thermoplastic in selective areas until it solidifies to form a first layer of the part to be made, which fuses to the cooled platen. The heat/cool element matrix is then heated to liquefy a very thin layer of cooled thermoplastic at the bottom of the newly solidified first layer so the cooled and solidified first layer releases from the build tray as the platen is raised and the tray is refilled with liquid thermoplastic. What is left on the platen is the first layer of the part being formed. The platen is then lowered onto the liquefied layer of thermoplastic, only slightly higher. A new layer can then be formed on the underside of the previous cooled layer. The process continues layer-by-layer until a complete part is formed.

The present invention can be used to make objects from nearly any material that passes through a liquid to solid phase, including water-ice.

DESCRIPTION OF THE DRAWINGS

The subsequent description of the preferred embodiments of the present invention refers to the attached drawings, wherein:

FIG. 1 shows a plan view of an apparatus according to an embodiment of the invention.

FIG. 2a shows a cross-sectional view of the apparatus shown in FIG. 1.

FIG. 2b is a representation of a coating process according to an embodiment of the invention in which the build tray is filled with a volume of liquid thermoplastic.

FIG. 3 shows a cross-sectional view of the apparatus shown in FIGS. 1 and 2, with a build tray filled with a film of liquefied thermoplastic.

FIG. 4 shows a cross-sectional view of the apparatus of FIGS. 1-3, with portions of the thermoplastic cooled and solidified forming a first layer of the part.

FIG. 5a shows a cross-sectional view of the apparatus of FIGS. 1-4 with a thin layer of liquefied thermoplastic at the bottom of the tray, allowing for the releasing of the first solidified layer of the part from the build tray as the platen is lifted upwards.

FIG. 5b is a representation of a re-coating process according to an embodiment of the invention in which the build tray is refilled with a volume of thermoplastic.

FIG. 6 shows a cross-sectional view of the apparatus of FIGS. 1-5, with the platen raised an additional amount, still holding the first layer of the part, and the build tray re-filled with another volume of liquid thermoplastic for formation of a subsequent layer of the part.

FIG. 7 shows a cross-sectional view of the apparatus of FIGS. 1-6 with portions of the second volume of liquid thermoplastic in the build tray being cooled and solidified to create a second layer of the part.

FIG. 8 shows a cross-sectional view of the apparatus of FIGS. 1-7, with a thin layer of liquefied thermoplastic at the bottom of the tray, allowing for the releasing of the second solidified layer of the part from the build tray as the platen is lifted upwards, the top of the second layer adhered to the bottom of the first layer.

FIG. 9 shows a cross-sectional view of the apparatus of FIGS. 1-8, with the build tray filled with a third volume of liquefied thermoplastic being selectively cooled to create a third layer of the part.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 a show plan and cross sectional area views of an apparatus according to an embodiment of the invention, in which platen 1 is arranged over a build tray 2 having a base that contains or is in contact with an array of Peltier-type hot/cold junctions 3 a-3 n. Build tray 2 also contains a heat sink 2 a that transfers heat to and from Peltier junctions 3 a-3 n via fan 2 d. Heated re-coater body 2 c holds a supply of liquefied thermoplastic 2 b. Platen 1 and may be raised and lowered over the build tray according to various steps in the invention.

FIG. 2b shows the re-coating process as re-coater body 2 c translates across the build tray 2 to deposit liquefied thermoplastic 2 b in the form of a thin film 4 onto the build tray 2. Heat sink and fan are not shown for simplification.

Referring to FIG. 3, a first step in a method according to the invention, after the build tray filled with a film of liquefied thermoplastic in FIG. 2b . Re-coater is not shown for simplification. Platen 1 is adjusted so that its bottom surface is in contact with a top surface of the thermoplastic film 4. Thermoplastic film 4 is heated uniformly by Peltier-type hot/cold junctions 3 a-3 f. Platen 1 is cooled at or below the solidification temperature of the thermoplastic.

In a next step, represented in FIG. 4, portions of thermoplastic film 4 continue to be heated to its liquid state by Peltier-type hot/cold junctions 3 d-3 f while other portions of thermoplastic film 4 are selectively cooled below its solid state by Peltier-type hot cold junctions 3 a-3 c. Solid zones 5 a-5 c created thereby become the first layer of the part to be additively manufactured. Platen 1 continues to be cooled at or below the solidification temperature of the thermoplastic.

Once the first layer of the part to be manufactured has solidified, the entire heating/cooling element matrix is energized to heat the thermoplastic material to create a thin liquid zone between the solidified first layer and the bottom of the build tray to allow the first layer to be separated from the build tray as the cooled platen 1 is lifted upwards. More specifically, thermoplastic film 4 is continues to be heated to its liquid state by Peltier-type hot/cold junctions 3 d-3 f. Thermoplastic film 4 is selectively heated above its liquid state by Peltier-type hot cold junctions 3 a-3 c to create thin liquid zones 6 a-6 c. At this point platen 1 begins to lift solid zones 5 a-5 c out of the liquid in the tray 4. Platen 1 continues to be cooled at or below the solidification temperature of the thermoplastic.

FIG. 5b shows a re-coating step as in FIG. 2b that occurs between every layer to refill the build tray as thermoplastic material is consumed by the object being printed. Platen 1 is raised to clear the Re-coater body 2 b. Re-coater body 2 b translates across build tray 2 to deposit liquefied thermoplastic 2 c in the form of a thin film 4 onto the build tray 2 to replace liquid depleted by removing solidified zones 5 a-5 c.

In a subsequent step, represented by FIG. 6, platen 1 lowers solid zones 5 a-5 c to the surface of the liquid in the tray 4, and intermediate zones 5 ab and 5 bc solidify between solid zones 5 a-5 c to complete the first layer of the part as platen 1 continues to be cooled at or below the solidification temperature of the thermoplastic. Thermoplastic film 4 continues to be heated to its liquid state by Peltier-type hot/cold junctions 3 a-3 f.

The process is then repeated, as represented by FIG. 7. Various heating/cooling elements in the matrix are energized to cool the thermoplastic liquid, and others are energized to heat the thermoplastic liquid, according to the build pattern of the part being manufactured to create a second layer of the part in the same way that the first layer was created (FIG. 4).

Once the second/subsequent layer of the part is formed/solidified, all of the heating/cooling elements of the matrix are caused to heat the thermoplastic material in the build tray to create a thin layer between the bottom of the second/subsequent layer and the build tray so that the platen can be lifted together with the solidified portions of the part to make room for yet another layer in the same way that the first layer was separated from the build tray (FIG. 5). Whereas elements 3 a, 3 b and 3 c were cooling in FIG. 7, they are switched to heating sufficient to create thin liquid zones 6 d, 6 e and 6 f (FIG. 8) so that the platen can lift the part away from the build tray to make room for refilling of the tray and creation of yet another layer (see FIG. 9). Re-coating occurs to replace thermoplastic liquid 4 that was depleted by removing solidified zones 6 a-6 c.

The process continues until the part has as many layers as required and may take place in any orientation, with or without the force of gravity. 

The invention claimed is:
 1. An additive manufacturing device comprising: a build tray with an array of heat exchange elements each of which are configured to independently and alternately heat and cool a respective area of the build tray; a moveable platen that lowers and raises into the build tray; a heated re-coater body moveably mounted between said build tray and said moveable platen and configured to apply successive layers of thermoplastic material to said build tray; said successive layers of thermoplastic material alternately solidified by the heat exchange elements of the build tray by cooling said thermoplastic material to create each layer of a multilayer part and then partially liquefied to release solidified thermoplastic material from the build tray as the moveable platen moves out of the build tray.
 2. The additive manufacturing device of claim 1 configured to operate in any orientation, with or without the force of gravity.
 3. The additive manufacturing device of claim 2 comprising a second liquefied thermosetting compound.
 4. The additive manufacturing device of claim 1 wherein the heat exchange elements are Peltier hot/cold junctions.
 5. The additive manufacturing device of claim 1 wherein the moveable platen is configured to be heated or cooled.
 6. The additive manufacturing device of claim 1 further comprising a temperature controlled enclosure surrounding the build tray and moveable platen. 